On January 4, NASA announced two new space missions to explore the solar system: Lucy, a probe that will visit swarms of ancient asteroids lurking near Jupiter, and Psyche, which will orbit the all-metal core of a dead planet.

These winners of the Discovery program, as it’s known, will each get $450 million to build their robots, plus a rocket to launch them.

“This is what Discovery Program missions are all about — boldly going to places we’ve never been to enable groundbreaking science,” Thomas Zurbuchen, the associate administrator of NASA’s Science Mission Directorate, said in a Jan. 4 press release.

But in a pile of rejected finalists, sitting alongside two conceptual missions to Venus, is a space telescope that might one day save countless lives on Earth from a killer asteroid: a threat Zurbuchen himself has said is “not a matter of if — but when.”

It’s called the Near-Earth Objects Camera, or NEOCam, and it promises to discover tens of thousands of rogue space rocks roughly 460 feet (140 meters) in diameter or bigger. That size is by design: Congress passed a law in 2005 charging NASA — as one of its seven explicitly stated goals — to find 90% of such near-Earth objects (NEOs) by 2020.

The reason is because asteroids and comets of this size are notoriously difficult to detect, yet can slug our planet or explode in our atmosphere with the energy of least 60 megatons’ worth of TNT. That’s more powerful than the largest nuclear weapon ever detonated.

“You do that over a city, and it’s a very, very bad day,” Mark Sykes, director of the Planetary Science Institute and a scientist on the NEOCam team, told Business Insider. “It’s important to look at your neighbourhood, from a planetary defence standpoint.”

While NASA did commit to partially fund NEOCam for a year, it’s effectively the space agency’s third pass on launching the telescope in a decade. (The mission was submitted in two previous rounds of Discovery.)

Meanwhile, NASA is running years behind its Congressional mandate to find NEOs, and Earth is mostly blind to threats that might one day level a city.

Just this past Monday, for instance, an asteroid possibly as large as a 10-story building flew past Earth closer than the moon at 9.8 miles per second (15.7 kilometers per second) — and yet astronomers only learned of its existence 2 days beforehand.

We live on a moving target for killer space rocks

NASA/JPL; WikipediaA radar image of asteroid 1950 DA, which is about half a mile wide and has a small chance of striking Earth.

Astronomers like to say Earth is drifting through a cosmic shooting gallery.

It’s no wonder why.

Any space rock that zooms within 125 million miles (200 million kilometers) of Earth is considered an NEO, and — so far — humanity has located about 15,500 such objects. Relative to Earth, the average one is about 30 million miles (50 million kilometers) away and moving between 27,000 mph (12 kilometers per second) and 45,000 mph (20 kilometers per second) — akin to flying the length of Manhattan once a second.

About 9% of these NEOs, or some 1,759 space rocks, are called “potentially hazardous” objects (PHOs), meaning they come within 4.6 million miles (7.48 million kilometers) of Earth.

The animation below, by Scott Manley, shows what the playing field looks like these days, and it is not comforting. Planets are teal (Earth is the third one from center), yellow and red show NEOs (red means they cross Earth’s orbit), and green shows more distant, main-belt asteroids:

But these are just the ones we know about.

Roughly 72% of all NEOs that are 460 feet (140 meters) or larger have not been found, according to the “National Near-Earth Object Preparedness Strategy“, a report published by the White House’s National Science and Technology Council (NSTC) in December 2016. This amounts to about 25,000 nearby asteroids and roughly 2,300 hazardous ones.

That doesn’t mean we shouldn’t be worried about smaller space rocks, though; in fact, quite the opposite.

“An asteroid much smaller, just 45 meters [150 feet] across, exploded in 1908 over Tunguska with an explosive energy of several megatons and destroyed an area as large as New York City,” Roger Blandford, a physicist at Stanford University, wrote in a September 2015 op-ed for Space News. “Congress calls these smaller asteroids ‘city killers,’ and although they are 30 times more numerous, we have located less than 1% of them.”

In raw numbers, “over 300,000 objects greater than 40 meters [130 feet] in size could be an impact hazard to the Earth and have not yet been detected,” according to NSTC’s report.

How NEOCam could help save Earth

If you’re a space rock, you reflect sunlight. Telescopes that are looking in the right place at the right time can see you as a dot sneaking across the blackness of space, allowing scientists to calculate your mass, speed, orbit, and the odds that you’ll smack into Earth.

If you’re a small NEO, though, you aren’t very bright. This means a telescope has to be very big and use very advanced hardware to find you — but big, bad telescopes are expensive and take a very long time to build and calibrate.

Take the Large Synoptic Survey Telescope (LSST), for example, which is one of Earth’s best current hopes of finding killer asteroids. The project broke ground in 2015 and is expected to cost upwards of $465 million to build. Based on its current construction schedule, it won’t be fully operational until late 2021, at the soonest, or able to fulfil the 90% detection goal set by Congress until the mid-2030s — more than a decade behind-schedule.

LSST, like all ground-based observatories, also comes with two major limitations.

The first: “You can’t see asteroids near the sun. You’re blinded by the sky,” Sykes said. “Right now we have to wait until those pop out in front of us. To get those guys, you really need to be in space — where you’re not blinded by the sky.”

Sykes said the other snag is that ground-based telescopes mainly rely on visible light for detection.

“If [an asteroid] has a dark surface, it’s going to be very hard to see,” he said.

NEOCam goes after these two problems by being in space, where no atmospheric gases get in the way, and by using an advanced, high-resolution infrared (IR) camera.

IR light is a longer wavelength of light that’s invisible to our eyes, but if a source is strong enough — say, a roaring fire — we can feel it as warmth on our skin.

Sun-warmed asteroids emit infrared light, even when they’re coasting through the void, or are too dark for ground-based telescopes to see. Which means NEOCam could spot them by their heat signatures.

The approach works. The prime example is NASA’s 8-year-old Wide-field Infrared Survey Explorer (WISE) telescope, which has found at least 230 NEOs and 42 PHOs from orbit.

However, it’s a less powerful telescope, has a smaller field of view, an older camera that requires cryogenic cooling (NEOCam’s does not), and wasn’t designed solely to hunt asteroids. While scientists gave it a new mission to do so in 2013, renaming the project NEOWISE, the telescope is scheduled to end operations in March 2017.

“[A] space-based observatory, working in concert with observations from ground-based telescopes, may be the best approach to detecting, tracking, and characterising the NEO population,” the NSTC’s December 2016 report states. “This combination would more rapidly complete the survey of objects larger than 140 meters [460 feet] while greatly improving our understanding of the hazard from the 50-140 meter [160-460 feet] NEO population.”

The NEOCam team proposed to launch in 2021 and find two-thirds of missing objects in the larger-than-460-feet (140 meters) category within 4 years — about a decade ahead of LSST’s schedule.

This would help address the NSTC’s concern on the issue:

“Finding NEOs as early as possible is the first priority for planetary defence, in order to give adequate time to make decisions and implement courses of action. This fact must be stressed: the earlier a NEO threat is detected, the better the emergency response to the threat will be.”

So if launching a capable replacement for NEOWISE is a priority, why didn’t NASA pick it?

The forces keeping NEOCam grounded

NASAAn illustration of a near-Earth object, or NEO, passing near Earth.

Only NASA knows why it didn’t pick NEOCam for launch, but it isn’t telling anyone, not even Sykes and his colleagues — at least not yet.

The space agency first wants to debrief the NEOCam team on the snags it saw with of its Discovery program proposal, a meeting that a NASA representative said will happen as early as next week.

“The Discovery review process identified strengths and weaknesses for all 5 mission proposals. As with Lucy and Psyche, NEOCam will be asked to address any issues that were raised in the review,” David Schurr, deputy director of NASA’s planetary science program, told Business Insider in an emailed statement.

During NEOCam’s debriefing, the space agency will “work and negotiate with the […] team” on a funding level for the next year, Jim Green, director of NASA’s planetary science division, told reporters during a Jan. 4 NASA teleconference.

“Whether it’s a drip or a flood, we’ll find out soon,” Sykes said.

After that year of funding runs out, however, all bets are currently off: NASA will have to “look for money” under a new presidential administration, according to Green, if it wants to keep the project alive. (“No flow, no go,” Sykes said.)

The hangup with NEOCam is not likely any lack of engineering prowess — “the rumour is that there were no major weaknesses [with the proposal],” one source who asked not to be named told Business Insider — but rather a bureaucratic technicality: a case of trying to jam a square peg into a round hole.

That’s because the mandate of NASA’s Discovery program is to pull off scientific “firsts” in the solar system.

An unprecedented mission to the metal core of a dead planet fits the bill, while a space-based asteroid detector is something humanity already tried with WISE (the NEO hunter launched in 2009).

But Sykes contends that NEOCam is a truly unique mission that could help NASA pull off its next planned era of crewed exploration — to near-Earth asteroids — by locating most of the remaining NEOs of interest.

“If we want to send people beyond low-Earth orbit, an asteroid costs much less than the surface of the moon or Mars,” Sykes said. “We can identify targets that are quick-turnaround times of weeks or months, to minimise the radiation exposure [in deep space] to astronauts.”

In addition, Sykes said, finding perhaps tens of thousands of new NEOs would lay more groundwork for efforts to mine asteroids for precious metals, gather fuel for deep-space exploration, and other novel (and scientific) human endeavours.

Former astronaut Ed Lu, who’s also a co-founder of the B612 Foundation — a group dedicated to launching its own NEO-detecting space telescope, called Sentinel — has grown impatient with the delays.

To get an asteroid hunter off the ground, Lu said, NASA needs to try something new, and fast.

“[T]here should be an open competition based on a planetary defence rather than a science requirement, as with the Discovery mission,” Lu told Business Insider in an email. “Detecting dangerous asteroids is a concern of national security, not just science.”

“[P]lanetary defence is currently treated as a scientific issue, and forced to compete with other science missions,” he wrote, “instead of being seen as a long-term imperative for the protection of humanity.”